Opposition to Obama's plan of limited, targeted airstrikes has surged 15 points in the past week, according to a new Pew Research Center/USA Today survey. The poll found that 63% oppose possible U.S. airstrikes in Syria, which is up 15 points from last week. Only 28% favor airstrikes, which is down a single point.

Most of the change from Pew's poll last week comes from previously undecided respondents making up their mind — which is a bad sign for an administration trying furiously to make its case before Congress will vote on whether to authorize a military campaign.

The biggest change, in fact, has come from Republican respondents. Last week, Republicans narrowly opposed airstrikes by a 35-40 margin. Now, they are against it by an astounding 21-70 gap. Democrats oppose such action by a 35-53 margin, and Independents oppose by a 28-66 gap.

A big part of the reason for the opposition comes from what respondents say is Obama's lack of clear explanation as to why the U.S. should wage the campaign of airstrikes. Only 35% of respondents said that Obama has "clearly explained why the U.S. should launch airstrikes," compared with 54% who said he has not.